The present invention relates to surface marker strips as for roadways, pavements and other surfaces, being more particularly directed to methods of providing better roadway-adhering and longer-life properties to such marker strips, and to marker strips or tapes with preformed ridges adhered to the roadways and the like of vastly improved integrity and life that, by reflection and/or retroreflection from the ridges, enable enhanced visibility, especially upon illumination by the headlights of approaching vehicles.
A paramount problem with preformed plastic pavement marker strips of the prior art is that of providing satisfactory adherence to the road surface under the constant heavy pounding of motor vehicle traffic. Unless the pavement marker has a deformable layer of elastomeric material which lacks memory positioned between the marker and the road surface, good adhesion will not always be achieved. This layer must deform readily and flow without memory into the irregular surface contours of the pavement. The deformability and ability to cold flow permits the absorption of the energy of vehicle tire impacts which would otherwise violently dislodge the pavement marker as the impact energy is dissipated. With an elastic material, adhesion to the road surface is weakened when the road is wet because the stretch-return action of such a memory material causes a pumping action to occur in which water-bearing dirt is forced between the material and the road surface. Dirt then becomes deposited between the adhesive material and the road surface and ultimately destroys the adhesive properties holding the pavement marker to the road.
While for some applications, techniques for adhesion of the type employed with marker strips of my earlier U.S. Pat. Nos. 3,920,346; 4,040,760; 4,069,787; 4,236,788 and 4,681,401 involving a thick mastic, provided a measure of the deformability and cold flow characteristics discussed above, for extensive use and under severe traffic and temperature varying circumstances, however, this technique proved at best to be only a compromise. Additionally, the mastic adhesive proved difficult to apply to the product in an economical manner. During extensive heat of summer, the adhesive had a tendency to flow readily as it became warm, with the result that the pavement-marker would creep or move with very heavy traffic. Sometimes the extremely low temperatures of winter, moreover, would reduce the bonding force between the adhesive and the pavement marker with the disastrous result of removal by snowplow action.
This problem of adequately securing a preformed plastic pavement-marker tape to the road surface was also recognized and partially solved in prior art U.S. Pat. Nos. 3,399,607; 3,587,415 and 4,117,192 and others. The techniques proposed in these patents involved base materials which exhibit desirable characteristics of deformability and lack of memory or cold flow which will provide conformability to the road surface and will absorb the shock energy of vehicular traffic. While useful for preformed flat surface pavement-marker tapes, however, such techniques do not adequately solve the problem for strips or tapes having preformed ridges such as those disclosed in my said earlier patents cited above. Because such prior art material has no memory and exhibits cold flow characteristics, any protuberance such as a ridge or wedge on the surface very quickly disappears when impacted by vehicular traffic so that the ridges flatten out and lose shape under the pressure of the vehicle tires. This, of course, defeats the primary purpose of high visibility of the protuberances or ridges at low viewing angles. If the ridges were comprised of a harder or more rigid material such as, for example, polyvinyl choride or epoxy or some other rigid or semi-rigid material, they would soon be engulfed by the non-memory cold flow characteristic of the base material under the pressure of the traversing traffic. Once depressed into the base material, the ridges would no longer protrude above a film of rain water and would thus be useless as high visibility ridges for wet night visibility.
As disclosed in U.S. Pat. No. 4,490,432 which incorporates the teachings of U.S. Pat. No. 4,388,359, an attempt was made to solve this problem by including reinforcing fibers with themix of the non-memory cold-flowing elastomeric base material. It was hoped that the fiber would offer sufficient stiffness to overcome the problem of losing the protuberances upon impact of high volume vehicular traffic. This, however, has not proven to be a completely successful solution; and in a short time, the protuberances become, in practice, flattened into the base material where they lose their function and utility.